Molecular Dynamics Investigated by Plasmon Rulers

Abstract

Plasmon rulers consisting of two connected gold nanoparticles respond to molecular distance changes with a spectral shift in resonance wavelength accompanied with a total intensity change. Here, I introduce the use of plasmon rulers as a single-molecule technique for the elucidation of conformational and stiffness changes in single polymers and proteins. The equilibrium fluctuations of a molecule’s extension are governed by intrinsic molecular properties. Monitoring plasmon ruler trajectories, I obtain the stiffness and extension of polyethylene glycol in varying salt concentrations of different cations. I observe a transition above about 1.2mM K+ ion concentration which is specific to potassium ions and does not occur in the presence of sodium ions. Further I investigate the conformational cycle of the molecular machine Hsp90. With the help of the plasmon ruler’s unprecedented observation bandwidth, I detect a third state inaccessible with other methods. This new state is characterized by dwell times in the order of dozens of seconds which are rare events only occurring in 1% of the cases. Further the influence of nucleotides on the protein is studied leading to a clear shift of the equilibrium.